Update Drop Shadow Styles

[scurker]

Shadows and fills can be used to show elevation. Our initial approach is to limit the number of shadows and provide the following semantic meaning:

Overlay = Any element that goes over content.
Raised = Any element that rests directly on the background / base or a sunken fill.

We should add 2 new global level variables for each of the new drop shadow styles:

--drop-shadow-overlay: 0 8px 8px -4px rgba(0, 0, 0, 0.04), 0 20px 24px -4px rgba(51, 51, 51, 0.08);
--drop-shadow-raised: 0 2px 4px -2px rgba(51, 51, 51, 0.08), 0 4px 8px -2px rgba(0, 0, 0, 0.04);

Overlay

All of the below components should inherit from --drop-shadow-overlay:

• Combobox
• OptionsMenu (+ future ActionMenu work)
• Dialogs/Alert/Modals
• LoaderOverlay
• BottomSheet

Raised

All of the below components should inherit from --drop-shadow-raised:

• Panel